This invention relates to a printer and, more particularly, to a printer for printing an image on a recording medium by using a line-type printhead.
As a typical conventional ink-jet printer, a serial printer is available, which is designed to sequentially print images by moving the printhead. laterally with respect to a conveying direction of a printing paper. A printer (line printer) using a line-type printhead having heating elements corresponding to one line is also known. For example, typical examples of such a line printer are a thermal printer using a line-type thermal head and a thermosensitive transfer printer.
Such a printer is generally constituted by a formatter for bitmapping PDL data sent from a host computer into an image to be actually printed, a mechanical portion of the printer, and an engine for controlling the mechanical portion.
When the ink-jet printing method is applied to this line printer, the following problems are posed in terms of data transfer:
(1) If the printer is constituted by the formatter and the engine as separate units as mentioned above, print data must be transferred to the printhead while vertical and horizontal synchronizations are established in the engine. For this reason, the engine requires a print buffer memory for receiving and storing print image data from the formatter. This print buffer memory has both a function of receiving print data from the formatter and a function of adjusting the transmission timing of print data to the printhead. The printer therefore requires a control circuit or the like for controlling access to such a memory. In addition, in a color printer, for example, this memory must store data for four colors. Furthermore, since an increase in printing density is required, a large-capacity memory is required as a print buffer. Moreover, with an increase in print speed, high-speed access to the memory is required, resulting in a complicated, expensive circuit arrangement.
(2) When a color print operation is to be performed by using line-type printheads for a plurality of colors, a function (registration adjustment function) of registering the print positions of the respective heads so as to accurately align the dot positions (nozzle positions) printed by the printheads for the respective colors is required. However, since such adjustment of the nozzle positions of the respective printheads must be realized on the order of .mu.m, it is difficult to mechanically adjust the nozzle positions.
(3) The ink-jet printer requires a cleaning operation (recovery operation) for the printheads at a predetermined timing. In the line printer, in particular, since the print data transfer operation and the print operation for the same data shift from each other by one line, if such a recovery operation is performed during a print operation, printing is performed with all the nozzles for one line. This operation, therefore, must be prevented.
The user may want to use such a line-type thermal head to print an image in an area narrower than the effective printing width of the thermal head (e.g., in a case wherein an image is to be printed on a postcard by using a line head having a width corresponding to A4-sized paper). In this case, data "0" is output to heating elements other than those in the print area.
If, for example, the bitmap memory has a data storage area corresponding to one A4-sized page, a print image is stored in a bitmap area corresponding to the postcard, while data "0" must be written in the remaining area. If, however, data which is not used for a print operation is stored in a given area of the bitmap memory in this manner, extra data bitmapping is required, resulting in a decrease in processing speed.
In addition, if heating elements which are not available for a print operation are arranged on portions near the right and left ends of the line-type printhead, data corresponding to the heating elements must be always stored as "0". In general, a memory device constituting a bitmap memory is expensive, and effective use of the memory is desirable. For this reason, it is not preferable in terms of specifications that data which is not used for a print operation be stored in the memory.